Fix typo in flymake.el of current emacs-25 branch

[Lele Gaifax]

Hi,

this is a micro fix to flymake.el::flymake-check-patch-master-file-buffer doc
string.

As English is not my native lang, I cannot tell whether the touched sentence
should really start with an "If" or "When" instead of... "Whether" :-)

  $ git diff
  diff --git a/lisp/progmodes/flymake.el b/lisp/progmodes/flymake.el
  index 11605bcf3a..1989a7b94d 100644
  --- a/lisp/progmodes/flymake.el
  +++ b/lisp/progmodes/flymake.el
  @@ -361,7 +361,7 @@ flymake-check-patch-master-file-buffer

   For example, foo.cpp is a master file if it includes foo.h.

  -Whether a buffer for MATER-FILE-NAME exists, use it as a source
  +Whether a buffer for MASTER-FILE-NAME exists, use it as a source
   instead of reading master file from disk."
     (let* ((source-file-nondir (file-name-nondirectory source-file-name))
            (source-file-extension (file-name-extension source-file-nondir))

thank you,
ciao, lele.
-- 
nickname: Lele Gaifax | Quando vivrò di quello che ho pensato ieri
real: Emanuele Gaifas | comincerò ad aver paura di chi mi copia.
address@hidden  |                 -- Fortunato Depero, 1929.